Methods have been proposed to indicate wetness in a diaper. For example, the inner surface (or the surface towards the body) of the outer liner of the diaper may have a printed message such as animal figures, alphabets, or other patterns attractive to infants. When the diaper becomes wet and the urine reaches the outer liner, the figure or pattern in the printed message will dissolve or otherwise become smudged. Such smudging will be visible to observers, thereby indicating that a diaper change is required.
Ink jet printing has been proposed for printing messages on the diaper outer liner. Ink jet printing is a well-known technique by which printing is accomplished without contact between the printing device and the substrate on which the printed characters are deposited. Briefly described, ink jet printing involves the technique of projecting a stream of ink droplets to a surface and controlling the direction of the stream so that the droplets are caused to form the desired printed image on that surface. This technique of noncontact printing is particularly well suited for application of characters onto substrates such as diapers.
In general, an ink jet ink composition must meet certain rigid requirements to be useful in ink jet printing operations. These relate to viscosity and resistivity of the ink, the solubility and compatibility of the components, and the wettability of the substrate. Further, the ink must be quick drying and smear resistant, and be capable of passing through the ink jet nozzle(s) without clogging, and permit rapid cleanup of the machine components with minimum effort. The printed message in many circumstances should resist abrasion.
Preferably, the ink composition should have short dry times when printed on fabrics, e.g., porous films, used as the outer liner of the diaper. In addition, it is preferred that the ink composition be suitable for printing in a binary array print head, which may have hundreds of nozzles. Further, the printed message should preferably dissolve (disperse or be removable) rapidly when contacted with a body fluid.
Although ink jet ink compositions have been proposed for printing on diapers for wetness indication, these compositions have one or more drawbacks. For example, they have long ink dry times, the printed messages do not remove rapidly when contacted with urine, or the quality of the printed messages is poor, for example, due to the formation of so-called “micro-satellites” or mist.
The foregoing shows that there exists a need for an ink jet ink composition for printing messages on diapers for wetness indication.
The invention provides such a composition. The advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.